text: #include "erfa.h"
  
  void eraPmat76(double date1, double date2, double rmatp[3][3])
  /*
  **  - - - - - - - - - -
  **   e r a P m a t 7 6
  **  - - - - - - - - - -
  **
  **  Precession matrix from J2000.0 to a specified date, IAU 1976 model.
  **
  **  Given:
  **     date1,date2 double       ending date, TT (Note 1)
  **
  **  Returned:
  **     rmatp       double[3][3] precession matrix, J2000.0 -> date1+date2
  **
  **  Notes:
  **
  **  1) The TT date date1+date2 is a Julian Date, apportioned in any
  **     convenient way between the two arguments.  For example,
  **     JD(TT)=2450123.7 could be expressed in any of these ways,
  **     among others:
  **
  **            date1          date2
  **
  **         2450123.7           0.0       (JD method)
  **         2451545.0       -1421.3       (J2000 method)
  **         2400000.5       50123.2       (MJD method)
  **         2450123.5           0.2       (date & time method)
  **
  **     The JD method is the most natural and convenient to use in
  **     cases where the loss of several decimal digits of resolution
  **     is acceptable.  The J2000 method is best matched to the way
  **     the argument is handled internally and will deliver the
  **     optimum resolution.  The MJD method and the date & time methods
  **     are both good compromises between resolution and convenience.
  **
  **  2) The matrix operates in the sense V(date) = RMATP * V(J2000),
  **     where the p-vector V(J2000) is with respect to the mean
  **     equatorial triad of epoch J2000.0 and the p-vector V(date)
  **     is with respect to the mean equatorial triad of the given
  **     date.
  **
  **  3) Though the matrix method itself is rigorous, the precession
  **     angles are expressed through canonical polynomials which are
  **     valid only for a limited time span.  In addition, the IAU 1976
  **     precession rate is known to be imperfect.  The absolute accuracy
  **     of the present formulation is better than 0.1 arcsec from
  **     1960AD to 2040AD, better than 1 arcsec from 1640AD to 2360AD,
  **     and remains below 3 arcsec for the whole of the period
  **     500BC to 3000AD.  The errors exceed 10 arcsec outside the
  **     range 1200BC to 3900AD, exceed 100 arcsec outside 4200BC to
  **     5600AD and exceed 1000 arcsec outside 6800BC to 8200AD.
  **
  **  Called:
  **     eraPrec76    accumulated precession angles, IAU 1976
  **     eraIr        initialize r-matrix to identity
  **     eraRz        rotate around Z-axis
  **     eraRy        rotate around Y-axis
  **     eraCr        copy r-matrix
  **
  **  References:
  **
  **     Lieske, J.H., 1979, Astron.Astrophys. 73, 282.
  **      equations (6) & (7), p283.
  **
  **     Kaplan,G.H., 1981. USNO circular no. 163, pA2.
  **
  **  Copyright (C) 2013-2017, NumFOCUS Foundation.
  **  Derived, with permission, from the SOFA library.  See notes at end of file.
  */
  {
     double zeta, z, theta, wmat[3][3];
  
  
  /* Precession Euler angles, J2000.0 to specified date. */
     eraPrec76(ERFA_DJ00, 0.0, date1, date2, &zeta, &z, &theta);
  
  /* Form the rotation matrix. */
     eraIr(  wmat);
     eraRz( -zeta, wmat);
     eraRy(  theta, wmat);
     eraRz( -z, wmat);
     eraCr( wmat, rmatp);
  
     return;
  
  }
  /*----------------------------------------------------------------------
  **  
  **  
  **  Copyright (C) 2013-2017, NumFOCUS Foundation.
  **  All rights reserved.
  **  
  **  This library is derived, with permission, from the International
  **  Astronomical Union's "Standards of Fundamental Astronomy" library,
  **  available from http://www.iausofa.org.
  **  
  **  The ERFA version is intended to retain identical functionality to
  **  the SOFA library, but made distinct through different function and
  **  file names, as set out in the SOFA license conditions.  The SOFA
  **  original has a role as a reference standard for the IAU and IERS,
  **  and consequently redistribution is permitted only in its unaltered
  **  state.  The ERFA version is not subject to this restriction and
  **  therefore can be included in distributions which do not support the
  **  concept of "read only" software.
  **  
  **  Although the intent is to replicate the SOFA API (other than
  **  replacement of prefix names) and results (with the exception of
  **  bugs;  any that are discovered will be fixed), SOFA is not
  **  responsible for any errors found in this version of the library.
  **  
  **  If you wish to acknowledge the SOFA heritage, please acknowledge
  **  that you are using a library derived from SOFA, rather than SOFA
  **  itself.
  **  
  **  
  **  TERMS AND CONDITIONS
  **  
  **  Redistribution and use in source and binary forms, with or without
  **  modification, are permitted provided that the following conditions
  **  are met:
  **  
  **  1 Redistributions of source code must retain the above copyright
  **    notice, this list of conditions and the following disclaimer.
  **  
  **  2 Redistributions in binary form must reproduce the above copyright
  **    notice, this list of conditions and the following disclaimer in
  **    the documentation and/or other materials provided with the
  **    distribution.
  **  
  **  3 Neither the name of the Standards Of Fundamental Astronomy Board,
  **    the International Astronomical Union nor the names of its
  **    contributors may be used to endorse or promote products derived
  **    from this software without specific prior written permission.
  **  
  **  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  **  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  **  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  **  FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  **  COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  **  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  **  BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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  **  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  **  LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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  **  POSSIBILITY OF SUCH DAMAGE.
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  */
  